The Two Together Railcard is in the new NFM data, it is £28 and can be bought from stations in the postcodes of Birmingham (B), Coventry (CV), Dudley(DY), Walsall (WS) and Wolverhampton (WV) and for use by two people who are both 16 years of age or older and where the first card holder lives in the trial area.
Discounts are available on Off-Peak (BVS, BVR, CDS, CDR, GDS, GDR, OPS, OPR,ODT,SCO, STO, SSS, SSR, SVS, SVR, SVH, 1DR, 1DT, SOP, PDS, PDR, SWS, SRR, C1R, CBA, WRE), Anytime (SDS, SDR, SOS, SOR, GOR, ADT, GPR), Advance (All first and standard types), some rail/sea journeys and also EFS, EFR, ELS, ELR, EOS, EOR, EVS AND EVR fares.
Discounts are not available between 0430 and 0930 Mon-Fri (except Public Holidays) and minimum fares apply to some travelcards.
Not valid on Eurostar, Season tickets, LUL services (except for travelcards), through journeys across London on tickets routed 'Via London', rail-air coaches, Oyster pay as you go, PlusBus and special excursions or charters and on some TOC specific or rail partnership fares.
The rest is pretty standard by the looks of it.
How does the Northern Duo work if one person travels? That is issued as one ticket covering two people, so it's impossible for the travellers to split their journeys (e.g. out together, return separately)....
Duo is issued as two sets of tickets, one at the price of the fare paid and one at zero fare.